Is Agriculture Sucking Fresh Water Dry? – ScienceNOW

The average American uses enough water each year to fill an Olympic-sized swimming pool, and global agriculture consumes a whopping 92% of all fresh water used annually. Those are the conclusions of the most comprehensive analysis to date of global water use, which also finds that one-fifth of humankind’s water consumption flows across international borders as “virtual water”—the water needed to produce a commodity, such as meat or electronics, if the ultimate consumers were to make it themselves rather than outsource its growth or manufacture.

The new study “is the most comprehensive and finest-resolution analysis to date,” says Sandra Postel, director of the Global Water Policy Project, which is based in Los Lunas, New Mexico.

Humans consume water in a number of ways: They pump it from rivers and reservoirs, draw it from underground aquifers, and render it unusable by polluting it, says Arjen Hoekstra, a water policy analyst at the University of Twente in Enschede, the Netherlands. Expanding on previous studies by them and others, he and colleague Mesfin Mekonnen analyzed humankind’s water footprint at high geographical resolution for the decade from 1996 to 2005, the most recent such interval for which comprehensive data are available. In the study, the researchers divided Earth’s surface into blocks about 85 square kilometers or smaller and then used data compiled by individual nations to estimate water-consumption patterns for all agricultural and industrial processes and for all household uses taking place in each.

Overall, humans used about 9087 cubic kilometers of fresh water—enough to flood the entire state of California with a little more than 21.4 meters of water—each year during that decade, Hoekstra and Mekonnen report online today in the Proceedings of the National Academy of Sciences. Just three countries—China, India, and the United States—are responsible for almost 38% of that water use, with footprints of 1.207, 1.182, and 1.053 cubic kilometers per year, respectively. Together, they have more than 44% of the world’s population.

Although the United States came in third on the list, it has less than 5% of the world’s population. So it led the world in annual per capita consumption of fresh water—which, including the amount of water needed to produce all of the goods and services the average American consumes, is a whopping 2842 cubic meters each year, more than enough to fill an Olympic-sized pool. Global average per capita consumption is about 1385 cubic meters per year.